[Musicianista]

What version firmware is in the Mackie's?
v2.12 is needed for HUI emulation.

You are definitely in HUI mode on the Mackies, right? (hold down the select buttons on channels 1 & 2 on each Mackie as you power them up, and press one of the rotary controllers with HUI in the LED to confirm.

I have an old Mackie Control with one Extender and they work fine. I had to upgrade the eprom chip in the MC to 2.12 though. The Extender was fine.

The Mackies running HUI are a compromise though, giving the chance of multiple banks of Extender faders, but with less functionality than a Command|8 which can't be more than 8 faders at a time.

Good luck.